Hydraulic actuator

ABSTRACT

A hydraulic actuator has a hydraulic cylinder with first and second pistons located therein. An inlet port formed in the hydraulic cylinder is connected to a source of hydraulic fluid and an outlet port connected to a hydraulic device to be actuated is formed in the hydraulic cylinder between the first and second pistons. A lever is mounted on the hydraulic cylinder to displace the first piston to increase pressure at the outlet port, to actuate the hydraulic device to be actuated and to displace the second piston when the pressure at the outlet port reaches a predetermined pressure so as to maintain actuation of the hydraulic device to be actuated.

United States Patent 1191 1111 3,813,883

Cords June 4, 1974 [54] HYDRAULIC ACTUATOR FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Frederick Cords, Lake Crystal 986,175 /1965 Great Britain 60/562 Minn.

[73] Assignee: Minnesota Automotive Inc., Primary Examiner-Edgar W. Geoghegan Mankato, Minn. Assistant Examiner-A. M. Zupcic Filed: June 18, 1973 gfjtglrlney, Agent, or F1rmMerchant, Gould, Smith & [2]] Appl. No.: 370,688

Related US. Application Data S RACT [63] Continuation of Ser. No. 202,850, Nov. 29, 1971, A hydraulic actuator has a hydraulic cylinder with first abandoned and second pistons located therein. An inlet port formed in the hydraulic cylinder is connected to a US. Clource of hydraulic and an outlet port connected hit. Cl. to a hydraulic device be actuated is formed in the [58] Fleld 0f Search 60/5 6 539, hydraulic cylinder between the first and second pis- 60/592, 572 tons. A lever is mounted on the hydraulic cylinder to displace the first piston to increase pressure at the outl l References Cited let port, to actuate the hydraulic device to be actuated UNITED STATES PATENTS and to displace the second piston when the pressure at 2,551,274 5/1951 MacDuff 60/572 the Outlet P reaches a predetermined Pressure as 3,068,651 12/1962 Shutt /562 to maintain actuation of the hydraulic device to be 3,l l7,42l l/l964 Stelzer 60/562 tuated.

3,583,160 6/197l Nakamura r 60/54.6 3,662,552 5/1972 Chiai et al. 60/562 7 Clams, 4 Drawlng Flgllres Z6 A 17 b PATENTED 4 1974 may 4/ INVENTOR.

FEEDER/CK VVfCoRos HYDRAULIC ACTUATOR This is a continuation of application Ser. No. 202,850, filed on Nov. 29, 197l, now abandoned.

BACKGROUND OF THE INVENTION For some time there has been a desire and need, in the automotive industry especially, for a remote hydraulic actuator to energize power take-off transmission accessory drives. Prior art shifting devices of this character now in use accomplish such shifting movements by the use of manual levers and linkages and/or by mechanism operated by either positive or negative air pressure. In either case, such devices have not been wholly satisfactory, the former due to reasons of frictional wear of the lever and linkages and the latter due to the high susceptibility thereof to air leaks in the vicinity of fittings and seals or the like. In addition, such air pressure devices must include expensive auxiliary equipment for creating the positive or negative air pressures. Further, such air pressure devices are particularly susceptible to freezing in lower temperature climates due to accumulation of water in the system. In the event of such wear factors and/or leaks in the above described gear shifting mechanisms it will be appreciated that slow engagement or disengagement of gears in a power take-off transmission may occur with severe stress loading of the edges of the gear teeth therein, even to a degree of fracture, thus causing expensive down time and replacement or repair of such transmiss|ons.

SUMMARY OF THE INVENTION With the disadvantages heretofore set forth in mind a primary object of the present invention is the provision of a hydraulic actuator which will cause positive engagement of the gears of the power take-off transmission upon actuation of the hydraulic actuator and which will maintain hydraulic pressure in the hydraulic actuator system subsequent to full actuation of the hydraulic device to be actuated.

A further object of the present invention is the provision of a device of the character above described which will prevent slow disengagement and stress loading of the gears of the power take-off transmission .in the event of minor leaks or the like in the hydraulic system.

A still further object of the present invention is the provision of a device of the character above described which is relatively inexpensive to produce, simple in construction, and extremely durable in use.

With the above objects in mind there is provided a hydraulic actuator having a hydraulic cylinder with an axial bore. A first and second piston is located in the hydraulic cylinder and with the hydraulic cylinder defines a fluid pressure chamber and a fluid reservoir chamber. An inlet port is formed in the hydraulic cylinder to communicate with the fluid reservoir chamber and is connected to a reservoir of hydraulic fluid. An outlet port is formed in the hydraulic cylinder between the first and second pistons to communicate with the fluid pressure chamber and is adapted to be connected to a hydraulic device to be actuated. A first spring is positioned between the first and second pistons to bias the first piston toward one end of the hydraulic cylinder and a second spring is positioned between the second piston and an opposite end of the hydraulic cylinder to bias the second piston toward the one end of the hydraulic cylinder. The second spring has a greater spring bias than the first spring and cooperates with the first spring to normally bias the first and second piston towards the one end to a retracted position. A valve is associated with the second piston and a valve stem associated with the first piston is biased in a direction tending to close the valve. A stop carried by the first piston is in a retracted position adjacent the one end of the hydraulic cylinder. A manually operated lever is mounted on the hydraulic cylinder to move the first piston against the bias of the first spring to close the valve carried by the second piston, to increase the pressure at the outlet port to the hydraulic device to be actuated and to move the second piston against the bias of the second spring to provide an accumulated pressure after the pressure at the outlet port reaches a predetermined value.

BRIEF DESCRIPTION OF THE DRAWING Referring to the drawings wherein like characters indicate like parts;

FIG. 1 is a diagramatic view of a vehicle equipped with a power take-off mechanism and a hydraulic system for engaging the gears thereof.

FIG. 2 is a view in longitudinal section axially of actuator valve of the hydraulic system shown in FIG. 1 with such valve in a retracted position;

FIG. 3 is a view similar to FIG. 2 with the parts thereof in an actuated position wherein the power takeoff mechanism is fully engaged and an accumulated pressure is applied to a hydraulic device to be actuated.

FIG. 4 is a fragmentary view in longitudinal section axially of the device to be actuated shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more specifically to the drawings, FIG. 1 thereof illustrates diagrammatically a vehicle, such as a truck 10, equipped with a conventional power takeoff transmission 11 for driving auxiliary equipment and a shifting mechanism or cap therefor indicated by the numeral 12. A hydraulic system, indicated generally by the numeral 15 is provided for shifting the shifting cap 12 in order to engage the gears (not shown) of the power take-off transmission 11 as will be described in more detail hereinafter. The hydraulic system 15 includes a hydraulic device to be actuated, in the nature of a slave cylinder 16, which is connected through a fluid conduit 17 to a hydraulic actuator indicated generally by the numeral 18, the hydraulic actuator 18 being in turn connected to a fluid reservoir 19 through a fluid conduit 20. .As seen particularly in FIG. 4, slave cylinder l6-includes a return spring 21, which moves the piston 22 of cylinder 16 in a direction to cause shifting cap 12 to disengage the gears of transmission 11.

FIGS. 2 and 3 of the drawings are longitudinal sections and illustrate a hydraulic actuator 18 which includes a hydraulic cylinder 25 having first and second piston means 26 and 27 located in anfaxially extended bore 24 defined by the cylinder 25. The first piston means 26 is positioned adjacent one end of the cylinder 25 and includes an axial projection 28 which projects exteriorly of the cylinder 25 through an opening 29 formed in such one end of the cylinder 25. Annular seal means 30 and 31 are positioned peripherally of the piston 26 and at the opening 29 so as to preclude exit of fluid through the opening 29. The opposite end of the cylinder is formed by a plug or the like 35, the second piston means 27 being located intermediate the first piston means and the opposite or plug end of the cylinder 25. Thus, with this arrangement, a first fluid chamber A is formed between the pistons 26 and 27 and the end plug 35. An annular seal positioned peripherally of the second piston 27 normally precludes escape of fluid from the fluid chamber A to the fluid chamber B during operation of the actuator valve 18.

An inlet port 42 is formed in the side wall of the cylinder 25 generally adjacent the opposite end or plug 35 thereof, and provides communication between the fluid chamber B and the reservoir 19 through the connection of fluid conduit 20 therebetween. An outlet port 41 is formed in the side wall of the hydraulic cylinder 25 between the first and second pistons 26 and 27, respectively, and provides communication between the fluid chamber A and a fluid chamber C in slave cylinder 16 through the connection of the fluid conduit 17.

A first spring means 43 is positioned between the first and second piston means 26 and 27 and a second spring means 44 is positioned between the second piston means 27 and the opposite end or plug 35 of the cylinder 25. The second spring means 44 is constructed to have a greater spring bias than the first spring means 43, for reasons which will become apparent hereinafter, and biases the second piston means 27 toward engagement with an annular stop ring 45. The annular stop ring 45 is positioned in the axially extended chamber 24 between the pistons 26 and 27 generally adjacent the outlet port 41. The spring means 43, being of a lesser bias than spring means 44, cannot overcome the bias of spring means 44 and move the piston 27 away from the stop ring 45, but merely biases the first piston 26 toward its retracted position at one end of the cylinder 25 during its normally inoperative condition of FIG. 2. In other words, the first and second pistons 26 and 27 are biased toward a retracted position, wherein the piston 22 of slave cylinder 16 is in a retracted position under the bias of the control or return spring 21 thereof, with the shifting cap 12 and power take-off transmission 11 in a disengaged condition.

A valve'means carried by the second piston 27 includes a valve port extending through the piston 27 between the fluid chambers A and B and an annular valve element of rubber-like material 51 forms a valve seat for the valve port 50 on the side of the second piston 27 adjacent the fluid chamber A. Means carried by the first piston means 26 precluding communication between the fluid pressure chamber A and fluid reservoir chamber B when the first piston 26 moves toward the second piston 27 includes a valve stem 55 having one end thereof slidably received within a cavity 56 formed in the first piston 26 so as to extend generally axially therein. Cavity 56 is a blind opening and has a coiled compression spring 57 positioned therein to extend between the closed end of the cavity 56 and the valve stem 55 so as to bias the valve stem 55 in a direction to seat the other end thereof against the valve seat 51. An annular stop ring 58 is positioned at the open end of the cavity 56 and forms means carried by the first piston means 26 for holding the other end of the valve stem in spaced relation to the valve seat 51 when the piston 26 is in its fully retracted position of FIG. 2.

In this manner, valve port 50 provides communication between the fluid chambers A and B so that fluid from the reservoir 19 may flow through the conduit 20, fluid chamber B, valve port 50 and into chamber A when the pistons 26 and 27 are in the retracted position of FIG. 2. Thus, any fluids within the slave cylinder 16, fluid conduit 17 and fluid chamber A which may escape therefrom either through natural dissipation, such as by evaporation or the like, or through accidental dissipation, which may occur due to seal deterioration or the like is replenished before the actuator valve 18 is to be utilized.

Manually operated means for moving the first piston means 26 against the bias of the first spring means 43, includes an actuating lever 60 having one end thereof pivotally mounted between a pair of ears 61 carried by the cylinder 25 adjacent the one end thereof. As shown, the axial projection 28 of the first piston 26 projects exteriorly of the cylinder 25 through the opening 29 between the ears 61 and is adapted to be engaged by a cam element 62 formed on one end of the actuating lever 60 at the pivot point thereof. As shown, the cam element 62 is so formed that movement of the actuator lever 60 in one direction positions the first and second piston means 26 and 27, in their retracted positions of FIG. 2 while movement of the actuator lever 60 about its pivot axis in an opposite direction positions .the first and second piston means 26 and 27 in their operative position of FIG. 3 wherein the second piston means 27 is positioned against an axially inwardly extending stop element 65 carried by the plug 35 and extending into the fluid chamber B.

It will be appreciated, that movements of the actuating lever 60 between the positions of FIGS. 2 and 3 causes initial movement of the piston 26 toward the piston 27 through engagement of the cam element 62 with the projection 28. Slight movement of the piston 26 in this direction causes valve stem 55 to be seated on valve seat 51 whereupon input flow from the reservoir 19 and fluid chamber B to the fluid chamber A is terminated. Further travel of the first piston 26 toward the second piston 27 displaces fluid from'the fluid chamber A through the outlet port 41, conduit 17 and to the slave cylinder 16. The piston 22 in the slave cylinder 16 is biased to resist pressure from the actuator valve by means of the return spring 21, the pressure developed by the first piston 26 being sufficient to overcome the force of this return spring 21 and to engage the gears in the power take-off transmission 11. This pressure, for purposes of explanation, is in the area of 50 to p.s.i. When the gears of the power take-off transmission 11 have been fully engaged and the shifting cap 12 resists further movement, additional movement of the first piston means 26 causes the second piston 27 to move from the position of FIG. 2 to the position of FIG. 3 wherein it is in engagement with the stop 65 and the spring 44 is in a compressed state. For purposes of explanation, approximately p.s.i. is required to start to overcome the force exerted by the springs 44 with the piston 27 exerting a pressure of a p.s.i. on the fluid in chamber A. when such piston 27 is moved to the position of FIG. 3 wherein the springs 44 are fully compressed. In the position of FIG. 3, second piston 27 effectively becomes an accumulator piston and exerts a continuing pressure under the bias of springs 44 against the fluid contained in the fluid chamber A through outlet 41, conduit 17 and against the piston 22 of the slave cylinder 16 so as to positively maintain the shifting cap 12 in a position to cause the gears of the power take-off transmission to be fully engaged at all times.

ln the event of slight leaks within the hydraulic system 15, it will be appreciated that the second or accumulator piston 27 will move from its position of FIG. 3 toward its position of FIG. 2 so as to maintain the gears of the power take-off transmission in their engaged state until such time as the pressure falls to a level wherein the gears will disengage rapidly. During such movement, it will be appreciated that the valve stem 55 will compress the spring 57 so asto be telescopically received into the cavity 56.

With the above arrangement of parts it will be seen that an extremely simple actuator valve, incorporating an accumulator system, has been provided for remote control shifting of power take-off systems or the like which will satisfy the objectives heretofore set forth and eliminate disadvantages which are inherent in systems presently used.

While I have shown and described a specific embodiment of this invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood, therefor, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

What is claimed is:

1. A hydraulic actuator adapted to be connected to a fluid reservoir and a hydraulic device to be actuated, said hydraulic actuator comprising:

a. a hydraulic cylinder defining an axial bore;

b. first and second piston means located in said bore of said hydraulic cylinder and defining a fluid pressure chamber between said first and second piston means and a fluid reservoir chamber between said second piston and one end of the hydraulic cylinder;

c. an inlet port formed in said hydraulic cylinder adapted to connect said fluid reservoir chamber to the fluid reservoir;

d. an outlet port formed in said hydraulic cylinder adapted to connect said fluid pressure chamber to the hydraulic device to be actuated;

e. activation means connected to said first piston means for displacing said first piston means to increase the pressure in said fluid pressure chamber for actuating a hydraulic device connected to said outlet port; and,

f. accumulator means connected to said second piston for resisting displacement of said second piston until the pressure in said pressure chamber reaches a predetermined value, and for providing an accumulated pressure in said fluid pressure chamber to maintain actuation of said hydraulic device.

2. A hydraulic actuator adapted to be connected to a fluid reservoir and a hydraulic device to be actuated comprising:

a. a hydraulic cylinder defining an axial bore;

b. a first piston means located in said bore adjacent one end of said hydraulic cylinder for movements toward the opposite end of said hydraulic cylinder;

c. a second piston means located in said bore between said first piston means and said opposite end of said hydraulic cylinder for limited movements toward said first piston means;

d. said first and second piston means with said hydraulic cylinder defining a fluid pressure chamber between said first and second piston means and a fluid reservoir chamber between said second piston means and said opposite end of said cylinder;

e. an inlet port formed in said hydraulic cylinder to communicate with said fluid reservoir chamber and adapted to be connected to the fluid reservoir;

f. an outlet port formed in said hydraulic cylinder to communicate with said fluid pressure chamber and adapted to be connected to the hydraulic device to be actuated;

g. first spring means located between said first and second piston means for biasing said first piston means toward a retracted position at said one end of said hydraulic cylinder;

h. second spring means located between said second piston means and said other end of said hydraulic cylinder for biasing said second piston toward said first piston to a retracted position, and for holding said second piston means in said retracted position until the'fluid pressure in said fluid pressure chamber reaches a predetermined value;

i. means associated with said first and second piston means providing communication between said fluid pressure chamber and said fluid reservoir chamber when said first and second pistons are in their retracted position and precluding such communication when said first piston is moved toward said second piston to create a fluid pressure at said outlet port; and

j. manually operated means for moving said first piston means against the bias of said first spring means for increasing pressure in said fluid pressure chamber and said outlet port, and for causing said second piston means to move against the bias of said second spring means when the pressure in said fluid pressure chamber reaches said predetermined value, so that said second piston means and second spring means provide an accumulated pressure in said fluid pressure chamber.

3. The structure of claim 2 in which said first piston means includes an axial projection and in which said hydraulic cylinder has an opening formed in said one end, said axial projection projecting through said opening to the exterior of said hydraulic cylinder.

4. The structure of claim 2, including means limiting the movement of said second piston means toward said first piston means, said means comprising an annular groove formed in said axial bore between said outlet port and said inlet port closely adjacent said outlet port and an annular snap ring received within said groove.

5. The structure of claim 2 in which said means associated with said first and second piston means providing communication between said fluid pressure chamber and said fluid reservoir chamber includes valve means carried by said second piston means, said valve means comprising a valve port extending through said second piston means from said fluid reservoir chamber to said fluid pressure chamber and an annular valve seat mounted on the side of said second piston means adjacent said fluid pressure chamber and in which said means precluding such communication when said first piston means is moved toward said second piston means to create a pressure at said outlet port comprises a valve stem, a blind cavity formed in said first piston means which opens in the direction of said fluid pressure chamber, said valve stem being slidably received in said cavity for limited movements toward said valve seat and a coil compression spring located in said cavity to bias said valve stem toward said valve seat.

6. The structure of claim including means limiting movement of said valve stem toward said valve seat when said first piston means is in its retracted position comprising an annular groove formed in said blind cavity at the end thereof adjacent said fluid pressure cham- 

1. A hydraulic actuator adapted to be connected to a fluid reservoir and a hydraulic device to be actuated, said hydraulic actuator comprising: a. a hydraulic cylinder defining an axial bore; b. first and second piston means located in said bore of said hydraulic cylinder and defining a fluid pressure chamber between said first and second piston means and a fluid reservoir chamber between said second piston and one end of the hydraulic cylinder; c. an inlet port formed in said hydraulic cylinder adapted to connect said fluid reservoir chamber to the fluid reservoir; d. an outlet port formed in said hydraulic cylinder adapted to connect said fluid pressure chamber to the hydraulic device to be actuated; e. activation means connected to said first piston means for displacing said first piston means to increase the pressure in said fluid pressure chamber for actuating a hydraulic device connected to said outlet port; and, f. accumulator means connected to said second piston for resisting displacement of said second piston until the pressure in said pressure chamber reaches a predetermined value, and for providing an accumulated pressure in said fluid pressure chamber to maintain actuation of said hydraulic device.
 2. A hydraulic actuator adapted to be connected to a fluid reservoir and a hydraulic device to be actuated comprising: a. a hydraulic cylinder defining an axial bore; b. a first piston means located in said bore adjacent one end of said hydraulic cylinder for movements toward the opposite end of said hydraulic cylinder; c. a second piston means located in said bore between said first piston means and said opposite end of said hydraulic cylinder for limited movements toward said first piston means; d. said first and second piston means with said hydraulic cylinder defining a fluid pressure chamber between said first and second piston means and a fluid reservoir chamber between said second piston means and said opposite end of said cylinder; e. an inlet port formed in said hydraulic cylinder to communicate with said fluid reservoir chamber and adapted to be connected to the fluid reservoir; f. an outlet port formed in said hydraulic cylinder to communicate with said fluid pressure chamber and adapted to be connected to the hydraulic device to be actuated; g. first spring means located between said first and second piston means for biasing said first piston means toward a retracted position at said one end of said hydraulic cylinder; h. second spring means located between said second piston means and said other end of said hydraulic cylinder for biasing said second piston toward said first piston to a retracted position, and for holding said second piston means in said retracted position until the fluid pressure in said fluid pressure chamber reaches a predetermined value; i. means associated with said first and second piston means providing communication between said fluid pressure chamber and said fluid reservoir chamber when said first and second pistons are in their retracted position and precluding such communication when said first piston is moved toward said second piston to create a fluid pressure at said outlet port; and j. manually operated means for moving said first piston means against the bias of said first spring means for increasing pressure in said fluid pressure chamber and said outlet port, and for causing said second piston means to move against the bias of said second spring means when the pressure in said fLuid pressure chamber reaches said predetermined value, so that said second piston means and second spring means provide an accumulated pressure in said fluid pressure chamber.
 3. The structure of claim 2 in which said first piston means includes an axial projection and in which said hydraulic cylinder has an opening formed in said one end, said axial projection projecting through said opening to the exterior of said hydraulic cylinder.
 4. The structure of claim 2, including means limiting the movement of said second piston means toward said first piston means, said means comprising an annular groove formed in said axial bore between said outlet port and said inlet port closely adjacent said outlet port and an annular snap ring received within said groove.
 5. The structure of claim 2 in which said means associated with said first and second piston means providing communication between said fluid pressure chamber and said fluid reservoir chamber includes valve means carried by said second piston means, said valve means comprising a valve port extending through said second piston means from said fluid reservoir chamber to said fluid pressure chamber and an annular valve seat mounted on the side of said second piston means adjacent said fluid pressure chamber and in which said means precluding such communication when said first piston means is moved toward said second piston means to create a pressure at said outlet port comprises a valve stem, a blind cavity formed in said first piston means which opens in the direction of said fluid pressure chamber, said valve stem being slidably received in said cavity for limited movements toward said valve seat and a coil compression spring located in said cavity to bias said valve stem toward said valve seat.
 6. The structure of claim 5 including means limiting movement of said valve stem toward said valve seat when said first piston means is in its retracted position comprising an annular groove formed in said blind cavity at the end thereof adjacent said fluid pressure chamber and an annular snap ring received within said groove, said valve stem including an annular shoulder engagable with said snap ring.
 7. The structure of claim 3 in which said manually operated means for moving said first piston means against the bias of said first spring means includes a lever pivotally mounted on said one end of said hydraulic cylinder engagable with said axial projection of said first piston means to move same toward said second piston means upon movement of said lever from a first position to a second position. 